The present invention relates to locking means for flexible elements. More particularly, the present invention relates to locking means for a flexible element to be wrapped and secured in cylindrical form. Typical of such elements is a cutting die blanket for use in conjunction with a cylindrical anvil roller in a rotary die cutting apparatus.
Rotary die cutting pertains to the art of cutting a moving workpiece, e.g. a continuously moving web or a sheet of material, without interrupting the movement of the workpiece. In typical application moving webs or sheets or material such as cardboard and corrugated paperboard are passed between a cutting roller and an anvil roller. Cutting elements known as cutting rules are mounted on the cutting roller for rotation therewith. The anvil roller is provided with a cylindrical cover known as a cutting die blanket which fits around the surface of the anvil roller and effectively increases its diameter by twice the blanket thickness. The axes of rotation of the cutting roller and the anvil roller are parallel and displaced by an amount such that at their points of closest proximity the cutting rules penetrate the surface of the die cutting blanket.
As the cutting rules penetrate the surface of the die cutting blanket a resistance to the penetration is developed which, for purposes of this application, is called a reaction force. Adjustment of the relative positions of the axes of rotation of the cutting die roller and the anvil roller is made to provide a degree of penetration and therewith a degree of reaction force sufficient to insure complete cutting of the moving web of material.
As will be recognized by those experienced in these arts, the amount of reaction force generated is not a function solely of the degree of penetration of the cutting rule but also of the resistance of the blanket material to penetration. Variations in the thickness of the blanket material have been a source of continuing difficulty for operators. More specifically, in order to insure that a complete cut is made each time a cutting rule comes in contact with a workpiece, the depth of penetration of the cutting rule into the blanket material is adjusted such as to generate adequate reaction force even at the points of least resistance to penetration notwithstanding that such low resistance areas comprise a relatively small portion of the blanket area. In order to insure adequate cutting over the entire blanket surface therefore, the depth of penetration for the major area of the die cutting blanket is greater than necessary thus causing excessive blanket damage and a shorter operating life.
It is for the foregoing reason that manufacturers of die cutting blankets employ techniques such as grinding and the like to insure a uniform thickness of blanket material thus minimizing the range of adjustment necessary to insure complete penetration and cutting of the workpiece.
One area of continuing difficulty, however, is the surface of the blanket in the vicinity of the joint. Known joints utilize securing means wherein the structure is such as to require a greater depth of blanket material. The utilization of certain of such blankets has resulted in the penetration setting being gauged to insure web cutting at the joint structure. The effect of this, as noted above, is unnecessarily deep penetration with attendant excessive wear over other areas of the blanket thus causing an unnecessarily short blanket life.
An approach to this problem has been to add additional material to the surface of the blanket above the joint area. Although prolonging the life of the blanket, this approach has caused a bump in the blanket resulting in objectionable vibrations and has also resulted in uneven blanket wear by reason of the intentional wear area developed at the joint. Further, where the bump in the blanket comes into register with a scoring die there has often resulted a cutting of the workpiece rather than the desired scoring. Needless to say such undesirable cutting results in significant losses.
There has also occurred unacceptable breakage of cutting rules by reason of the bumps heretofore described. Such breakage results from excessive pressures on the cutting rules by reason of the deep penetration of the "bumps."